Measuring the torsional forces acting on a shaft, particularly a power shaft, is often desirable. Such shafts are often found in hydraulic power units. Hydraulic power units such as pumps, motors, and transmissions are used to convert and transmit power between devices in many types of equipment. For example, a hydraulic pump may convert the power of an internal combustion engine or other source into a flow of high pressure hydraulic oil that can be used for performing a useful function in a machine. This flow of high pressure oil may be used to power a hydraulic motor that propels a wheel or track in a vehicle such as a tractor, bulldozer, or crane. In other instances this flow of high pressure oil may be used to operate hydraulic cylinders that perform such functions as manipulating the excavation bucket on a back hoe or for another device.
The primary measurements that are useful for determining performance and controlling hydraulic power units are the fluid pressure, fluid flow, shaft rotation speed, and shaft torque. Pressure, flow, and speed are routinely measured with readily available sensors. In the past, pressure and flow sensors have been integrated into hydraulic power units such as hydrostatic pumps and motors. Examples of using speed sensors are given in U.S. Pat. No. 5,325,055.
Several technologies are available for measuring the torque experienced by a rotating shaft. In one common technology, a series of strain gauges are bonded in strategic locations to the shaft. The electrical signals that are produced by these strain gauges are often transferred from the rotating shaft to the fixed portion of a machine through a series of slip rings. In another common embodiment of torque sensing, rotary transformers are used to provide power to the rotating electrical circuit and also to transfer the measured torque signal from the rotating shaft to the non-rotating portion of the machine. Another torque measurement system involves the attachment of a small radio transmitter and power supply to the rotating shaft. With such a radio telemetry system, the torque is normally measured by strain gauges then transmitted by analog or digital radio signals to a receiver positioned on the stationary portions of a machine.
Torque measurement systems which have been used with hydraulic power units such a hydrostatic pump or motor generally suffer from all of the following:
High cost
Large size
Poor reliability
Impracticality for serial production
Lack of integration with the hydraulic power unit
When rotating shaft type torque transducers have been used in the past with hydraulic power units such as hydrostatic pumps and motors, their high cost and large size has limited their use to that of testing during the product development phase. Non-contact torque transducers have not been integrated within a hydraulic power unit nor have they been incorporated into such a unit for serial production.
In the prior art cited above, all torque sensing systems are xe2x80x9ccontactxe2x80x9d methods as opposed to xe2x80x9cnon-contactxe2x80x9d methods. In these cases, an electronic transducer, and often signal conditioning or conversion electronics are attached to the rotating shaft. The xe2x80x9ccontactxe2x80x9d methods of torque measurement have the deficiencies cited above.
Non-contact torque transducers have also been developed in the prior art. An example of such a device is shown in U.S. Pat. No. 5,052,232. In this system, the rotating shaft is circularly magnetized in such a manner that a measurable axial magnetic field is created outside of the shaft which is indicative of the torque experienced by the shaft. While this system provides a non-contact means of torque measurement, such torque transducers have been only used with hydraulic power units as an external module which is separate from the hydraulic power unit, not integrated into the hydraulic power unit, and can be connected to any power unit for laboratory testing or for whatever purpose. The prior art has not demonstrated the integration of a magnetoelastic torque transducer into a hydraulic power unit.
In other prior art, the shaft torque of a hydraulic power unit has been estimated by the following formula:   τ  ≈                    d        ·        Δ            ⁢              xe2x80x83            ⁢      p              2      ·      Π      ·      e      
This formula is used to estimate torquexcfx84 where the displacement d is either known or measured, differential pressure xcex94p is measured, and e is the torque efficiency of the power unit. This formula only provides an estimate of torque since the torque efficiency xe2x80x9cexe2x80x9d is affected by many factors that are not readily ascertainable under operation. Therefore, there are a number of problems associated with determining and controlling or limiting the torque that is experienced by the shaft of a hydraulic power unit.
Therefore, it is a primary object of the invention to provide an improved system and method for determining the torque of hydraulic power units such as hydraulic pumps, hydraulic motors, axial piston pumps, axial piston motors, radial piston pumps, radial piston motors, gear pumps, gear motors, vane pumps, vane motors, roller vane pumps, roller vane motors, gerotor pumps, gerotor motors, geroller pumps, geroller motors, swash plates, valves, or hydraulic actuators of any kind.
A further object of the invention is to provide a system and method for the integration of a non-contact torque transducer into a hydraulic power unit such as the types described above.
Another object of the present invention is to provide a method for integrating such a non-contact torque transducer into a hydraulic power unit.
Yet another object of the invention is to provide for integrating a magnetoelastic torque transducer into a hydraulic power unit.
A still further object of the invention is to provide a set of specific regions of the shaft within a hydraulic power unit that may be circularly magnetized for use as part of a magnetoelastic torque transducer.
Another object of the invention is to provide a system and method for integrating a torque transducer with a speed transducer and then integrating these into a hydraulic power unit.
A further object of the invention is to integrate a torque transducer and a speed sensor within a single sensor.
Yet a further object of the invention is to provide a system and method for integrating a torque transducer with a ball bearing, roller bearing, sleeve bearing, plain bearing, or other bearing.
Another object of the invention is to provide a system and method for producing a speed and torque sensing transducer that is integrated into a ball bearing, roller bearing, journal bearing, plain bearing, or other bearing.
A further object of the invention is to provide a method of producing a ring of material in place on a shaft rather than producing the ring separately and installing it onto the shaft.
These and other objects of the invention will become apparent from the following description.
This invention relates to an apparatus that consists of a hydraulic power unit such as a hydraulic pump, motor, or transmission with an integrated non-contact torque transducer. The term xe2x80x9cintegratedxe2x80x9d as used herein means that the transducer is contained within. The unit is an integral part thereof, usually at the time of manufacture. Additionally, the invention relates to a method for integrating a circularly magnetized torque transducer into such a hydraulic unit. The invention further relates to the integration of both a torque sensor and a speed sensor into such a hydraulic power unit. Additionally, the invention relates to a method of integrating a torque transducer into a bearing. Finally, the invention relates to an enhanced method of manufacturing a torque transducer.
The invention is a hydraulic power unit such as a hydraulic pump or hydraulic motor with an integrated non-contact torque transducer. The integrated torque sensor uses magnetoelasticity, magnetostriction, stress wires, xe2x80x9cguitar stringxe2x80x9d elements, strain gauges, surface acoustic waves, acoustic, light, optical, capacitance, inductance, resistance, reluctance, radio telemetry, strain members, charge coupled devices, or micromaching to make a non-contact determination of the torque in a shaft. Such a device is capable of sensing the torque in the shaft of a hydraulic power unit such as a hydrostatic pump or motor, and may optionally be adapted for sensing the speed of rotation or instantaneous rotational position of such a unit. A control system that is capable of sensing the measurement of the torque transducer, and possibly other information may optionally be used to control the torque on a hydraulic power unit. As this additional information concerning torque and speed of a hydraulic power unit is measured, improved control and other improvements result.
The preferred embodiment could use a magnetoelastic torque sensing technology. In magnetoeleastic torque sensing technology, a region of appropriate magnetic material which makes up the shaft or is attached to the shaft is circularly magnetized. Under a torque induced strain, the circularly magnetized magnetic material will experience a distortion in magnetic domains. This distortion of magnetic domains results in an axial magnetic field with a magnitude and direction which is indicative of magnitude and direction of the applied torque.
The preferred embodiment further uses a series of features that are spaced around the circumference of the shaft. An appropriate sensing means is further used to sense the passing of these features as the shaft rotates. By sensing the time between passing of these features, or by measuring the frequency with which these features pass the sensor, the rotational speed of the shaft is determined. An example of speed sensing in a hydraulic power unit without torque measurement is given in U.S. Pat. No. 5,325,055. An example of combined speed and torque sensing is shown in U.S. Pat. No. 5,591,925. Neither of these patents contemplate integration of a non-contact torque and speed sensor into a hydraulic power unit.
The data obtained from an integrated non-contact torque and speed sensor is used to improve machine operation in several ways. First, this information is used to limit the torque of a hydraulic power unit. Torque may be limited for the purpose of protecting a load from damage or preventing the stalling of an internal combustion engine. Second, this information is used for the purpose of enhanced control. Measured torque information is useful in various control schemes which are sometimes designed to enhance traction and reduce or prevent wheel slippage, or for other purposes.
In particular, the present invention provides for control of a hydraulic system which incorporates an integrated torque transducer which is capable of measuring actual torque, as opposed to merely estimating torque through calculations which are based on other measured and estimated quantities. As torque is directly measured by the apparatus of the present invention, the information needed for improved control and monitoring is available.